In the production of titanium tetrachloride, raw materials, including ilmenite or rutile ores or other titanium-rich materials such as those obtained from beneficiating these ores, are reacted with chlorine under reducing conditions to yield a mixture of metal chlorides from which titanium tetrachloride may be recovered.
Aluminum chloride is present in the chlorination product of practically every case where aluminum compounds are present in the raw materials. Aluminum chloride present in the crude titanium tetrachloride is a highly corrosive material. It both quickly and severely attacks the metal materials of construction in the purification systems.
Prior art has taught methods by which aluminum chloride present in the crude titanium tetrachloride may be passivated, meaning the aluminum chloride is converted to a less corrosive or non-corrosive compound.
U.S. Pat. No. 2,600,881 to Kay and Rick teaches the addition of water to the crude titanium tetrachloride. According to this patent, water is added in an amount that is sufficient to react with only the aluminum chloride present in the crude titanium tetrachloride. Water reacts with the aluminum chloride and converts it to a less volatile, non-corrosive hydrate or oxychloride. Although this patent teaches a method of passivating the aluminum chloride, there continued to be a major disadvantage. If water was added in excess of that amount just sufficient to remove the aluminum chloride, the excess water reacted with the titanium tetrachloride converting it to hydrolysis products resulting in losses of titanium value. This patent offered no teaching or suggestion as to how to avoid the addition of excess water or how to accommodate the variations in aluminum chloride content of crude titanium tetrachloride that may be experienced in a continuous industrial process.
It was reported in U.S. Pat. No. 4,125,586 to Glaeser that to successfully apply the method taught in U.S. Pat. No. 2,600,881 on a commercial scale required that at least 10% excess water be added in order to effectively passivate the aluminum chloride. As an improvement to reduce losses of titanium value, U.S. Pat. No. 4,125,586 taught that loss in titanium value could be essentially eliminated by adding a mixture of water and sodium chloride to the crude titanium tetrachloride. The water addition was made in an amount less than that needed to convert all the aluminum chloride present to aluminum oxychloride; but the sum of the total amounts of water and sodium chloride added was in excess of that amount needed to react with the aluminum chloride present.
While U.S. Pat. No. 4,125,586 was an improvement, there was still the need to have a method that could control passivation of aluminum chloride present in the crude titanium tetrachloride at a process aim point reducing both the losses of titanium value and the corrosion.
U.S. Pat. No. 4,070,252 to Bonsack teaches a method for separating niobium and/or tantalum chlorides from a liquid crude titanium tetrachloride vehicle by adding water to the crude titanium tetrachloride vehicle in a portion not substantially above 1 mole per mole of these chlorides. Bonsack teaches that the addition of water in his process may be made before or after the chlorination reaction.
Even in view of the teachings of the art cited above, an accurate, in-process control method was needed that could respond to the demands of continuous plant operation where there are variations in the aluminum chloride content of the crude titanium tetrachloride due to (1) variations in the uniformity in the distribution of the aluminum containing minerals in the ore being processed; (2) variations in the rate at which ore is processed; (3) variations in aluminum content from one ore source to another; (4) variation in the content of mineral species other than those containing aluminum and titanium that consume the passivating agent; and (5) variation in the amount of aluminum chloride removed with any initial separation of higher boiling metal chlorides from the product titanium tetrachloride vapor.
An in-process, real time control loop capable of controlling the passivation of aluminum chloride formed in the chlorination of titanium-containing ores by monitoring titanium oxychloride present in passivated crude titanium tetrachloride comprising the steps:
(a) rapidly mixing into a chlorinator discharge stream, where the stream comprises predominately vapor in the presence of liquid mist and solids, an aluminum chloride-passivating agent to form in the process stream an essentially non-corrosive aluminum containing compound, and titanium oxychloride;
(b) measuring in-process the concentration of titanium oxychloride in the chlorinator discharge stream or in the crude titanium tetrachloride.
(c) comparing the measured concentration of titanium oxychloride to that of an aim point concentration of titanium oxychloride; and
(d) adjusting the rate of addition of the aluminum chloride-passivating agent to restore or maintain the concentration of titanium oxychloride at the aim point.
The aluminum chloride-passivating agent is selected from the group consisting of water, water containing solutions, water containing mixtures, and carboxylic acids.
In the present process it is preferred to measure the concentration of titanium oxychloride by an optical method selected from the group consisting of transmission filter Infrared spectroscopy, transmission Fourier Transform Infrared spectroscopy, Raman spectroscopy, Attenuated Total Reflectance Infrared spectroscopy, and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy.
It is also preferred that the measurement of the concentration of titanium oxychloride be made in a frequency range of from 800 to 2000 cmxe2x88x921.
It is most preferred that the concentration of titanium oxychloride is measured by diamond based Attenuated Total Reflectance Fourier Transform Infrared at a frequency of about 820 cmxe2x88x921.